1. Field of the Invention
Aspects of the present invention relate to a membrane electrode assembly for a fuel cell, and more particularly, to a membrane electrode assembly for a fuel cell including a diffusion layer and/or a supporting layer selectively containing one or more of a hydrophilic material, a hydrophobic material, a porous material, a hydrous material, and the like that are required to improve the performance of the fuel cell.
2. Description of the Related Art
A fuel cell is a type of energy generating system in which energy from a chemical reaction between hydrogen and oxygen, or between hydrogen contained in a hydrocarbon-based material, such as methanol, ethanol, or natural gas, and oxygen is directly converted to electrical energy. Fuel cells can be categorized as phosphoric acid type fuel cells, molten carbonate type fuel cells, solid oxide type fuel cells, polymer electrolyte membrane fuel cells, alkali type fuel cells, and the like, according to the electrolyte that is used. These fuel cells operate on the same principle, but have different fuels, different operating temperatures, different catalysts, and different electrolytes.
A fuel cell stack that substantially generates electricity in a fuel cell system generally has a stack structure including a plurality of unit cells including membrane electrode assemblies (MEAs) and separators or bipolar plates. An MEA has a structure including: an anode, i.e., a fuel electrode or an oxidation electrode; a cathode, i.e., an air electrode or a reduction electrode; and a polymer electrolyte membrane interposed therebetween.
That is, an electrolyte membrane is located at the center of the MEA, and electrodes, in particular, a cathode and an anode, are disposed on respective sides of the electrolyte membrane. Each electrode includes a catalyst layer, a diffusion layer, and a supporting layer. In a conventional fuel cell, current collectors that collect the current generated in the electrodes and transfer the collected current to outer circuits are located outside of the supporting layer. Thus, the diffusion layer and the supporting layer in the conventional fuel cell must be electrically conductive so that the current generated in the catalyst layer can flow to the current collectors.
Meanwhile, the diffusion layer and the supporting layer can be porous, in order to distribute materials, hydrophobic, in order to rapidly discharge the generated water, or hydrophilic and/or hydrous, in order to smoothly supply water. However, since the materials forming the diffusion layer and the supporting layer in the conventional fuel cell must also be electrically conductive, the choice of materials forming the diffusion layer and the supporting layer is necessarily limited, and thus, the performance of the fuel cell is limited.
Research so far has focused only on improving the physical properties of diffusion layers and supporting layers that are electrically conductive. There has been no research focused on developing non-conductive materials for the diffusion layer and the supporting layer, an avenue of research that is made possible by changing the location of the current collectors as described herein.